Transformer protective apparatus



May 19, 1953 E. H. YONKERS 2,639,346

TRANSFORMER PROTECTIVE APPARATUS Original Filed Sept. 25. 1948 2Sheets-Sheet l I IN V EN TOR.

Eda/a rdHYmz/zerq B Y KM m v r May 19, 1953 E. H. YONKERS TRANSFORMERPROTECTIVE APPARATUS Original Filed Sept. 25, 1948 2 Sheets-Sheet 2VENTO a 0 6 mm m W; Z W fimm V. r m .w w

m MW Eda/adj? Patented May 19, 1953 TRANSFORMER PROTECTIVE APPARATUSEdward H. Yonkers, Glencoe, Ill., assignor to Joslyn Mfg. & Supply 00.,Chicago, Ill., a corporation of Illinois Original application September25, 1948, Serial No. 51,236, now Patent No. 2,572,901, dated October 30,1951. Divided and this application September 20, 1951, Serial No.247,442

4 Claims.

The present invention relates to protective apparatus and moreparticularly to improvements in apparatus for protecting apole-supported electrical distribution transformer and for disconmeetingthe transformer from its current supply line when a fault occurstherein. This application is a division of applicants copendingapplication, Serial No. 51,236, filed September 25, 1948, now Patent No.2,572,901, dated October 30, 1951, and assigned to the same assignee asthe present invention.

. Apparatus for the purpose described is in certain installationsmounted directly upon the housing or tank of the transformer which it isused to protect and conventionally includes entirely independentlightning arrester and fused cutout units for protecting the transformerprimary winding against damage occasioned by lightning surges andoverload conditions, respectively. In commercial practice few attemptshave been made to provide a single unitary device for providing completetransformer protection against dangerous over-voltage and overloadswhile at the same time providing the usual feature of protecting theline against a short circuit caused by a fault in the transformer. As aresult, the cost of providing and maintaining commercially availableprotective equipment is relatively high.

It is an object of the present invention, therefore, to provide animproved combination arrester-cutout unit of low cost construction whichmay be easily and quickly installed on any electrical distributiontransformer of standard commercial construction, is easy to refuse andfully protects the transformer against damage by lightning surges andoverload condition.

It is another object of the invention to provide for use in acombination arrester-cutout unit, an improved fused cutout of simple lowcost construction which may be easily and quickly installed upon theavailable supporting facilities of a standard electrical distributiontransformer.

The present invention, both as to its organization and method ofoperation, together with further objects and advantages thereof, willbest be understood by reference to the following specification taken inconnection with the accompanying drawings in which:

Fig. 1 is a top perspective View of a conventional electricaldistribution transformer equipped with the present improved protectiveapparatus; V

Fig. 2 is a side perspective view of the transformer and protectiveapparatus illustrated in Fi 1; 'T

Fig. 3 is a shortened front perspective view of the spring arm forming apart of the cutout embodied in the protective apparatus;

Fig. 4 is a side edge view of the spring arm shown in Fig. 3;

Fig. 5 is a side View partially in section illustrating the structure ofthe fuse link assembly forming a part of the cutout embodied in theprotective apparatus; and

Fig. 6 is an enlarged view of a portion of Fig. 5 better illustratingcertain of the components of the fuse link assembly.

Referring now to the drawings, and more particularly to Figs. 1 and 2thereof, the present improved protective apparatus is there illustratedas comprising a combination lightning arrester and fused cutout unitsupported by the existing supporting facilities of a standard electricaldistribution transformer 10. Specifically, this transformer comprisestwo sets of supporting brackets H and [2 which are arranged inspaced-apart relationship around the sides of the transformer tank toproject radially therefrom, are fixedly mounted upon the transformertank and are adapted for alternative use in supporting the tank upon asupporting pole or similar supporting structure. The purpose ofproviding two sets of brackets is to facilitate connection of secondarycircuit conductors to the secondary terminals of the transformer (notshown) which are brought out through a terminal block disposed along thehidden side of the transformer tank approximately midway between thebrackets. As best shown in Figs. 1 and 2 of the drawings, thetransformer is also equipped with the usual bushing insulator l3 whichprojects upwardly from the top of the transformer tank and servesinsulatingly to support the usual terminal stud [8. This stud and theunused set of supporting brackets II and I2, are employed to support allparts of the present improved combination arrester-cutout unit.

In brief, this unit comprises a self-contained lightning arrester [4a,the parts of which are housed within a petticoated insulator [4, a fusetube assembly [5, a terminal subassembly 16 for supporting the fuse tubeassembly for pivotal swinging movement about the long axis of the studI8 and a stationary terminal assembly H with which the contact providedat the swing end of the fuse tube assembly 15 is latchingly engageable.More specifically, the electrode structure of the lightning arrester Ila shown in dash lines in Fig. 2 of the drawings is housed within acavity extending upward from the lower end of the insulator I4.Preferably, this arrester is of the improved expulsion type disclosedand claimed in Patent No. 2,1643% granted July 4, 1939, to Ralph E.Pittman. Among other elements it comprises a pair of spaced electrodes.one of which is connected to a conductive rod i ioextending through theinsulator i i to the upper end thereof to support the terminal assembly27-, and the other of which is connected to a gap electrode Me.

For the purpose of adjustably supporting the insulator it and associatedparts in a desired vertical and horizontal position upon either of thetwo sets of radially extending brackets l :l and 12, two cooperatingbrackets 59 and 19d are provided. More specifically, the two cooperatingbrackets is and We are constructed and arranged in the exact mannerdisclosed and claimed in applicants prior Patent No. 2,508,055; grantedMay 16, 1950. The construction is such that the insulator it may besupported upon either of the two transformer brackets H and S2 at anydesired elevation, within limits, and any desired angular setting. Thearrangement is also such that the electrode lie of the arrester assemblycounts with the supporting bracket It to provide an isolating gap whichis appropriately designed as to length to prevent system current leakagethrough the arrester.

As indicated above, the cutout assembly conipris es a bracket l6 mountedupon the terminal conductor Mb of the insulator H3 at the upper end'oithis insulator and a spring arm I? mounted upon the bushing conductor orstud iii of the transformer assembly. Preferably, the bracket It is ofarcuate configuration and is fixedly mounted upon the terminal conductorMb by means of a nut Hid threaded onto this conductor. As will beevident, the angular setting of the bracket IS relative to the insulatorIll may be adjusted as desired by rotating thisbracket about theterminal conductor l ib. At its extended end, the bracket 1 6 isprovided with a pair of cars IGct and lob which are spaced apart todefine an opening or slot I80 for receiving one of the pig'- tailferrules of the fuse link assemblyin the manner more fully explainedbelow.

As best shown in Figs. 3 and 4 of the drawings,

21 in mounting the arm i1 upon the transformer bushing stud 18. Thelower end portions of the spring arm laminations Ha and Eli) areanchor'ed within the slotted head We of the "piece Ebbymeans'oi a rivet22 extending through registering openings in the two laminations and thehead part 2601. of the piece 2i]. In order to increase theresiliency ofthe laminations, thereby to provide the desired tension upon the fuselink l -supported between the extended end of the arm ll and the bracket"l8, lamination Ha is provided with elongated weakening slots 23longitudinall'y spaced apart along the upper part of this arm laminationand the lamination I-1b is similarly provided with elongated weakeningslots 2 4'throu'ghout the length thereof. The'short lamination i'lb actsas "a damping element to damp out oscillation of the arm 11 in responset'o'rele'ase of the'arm it from thedeform'ed-closed circuit positionthereof illustrated in Fig. 2 "of the drawings whichoccurs incident torupture-of i the fusible element forming a part of the fuse link 15.Maximum effectiveness of the short lamination ill) to. perform thisassigned function is obtained by tying the upper end of this laminationto the adjacent section of the long lamination llc in such manner as topermit relative sliding movement therebetween. To this end, a rivet 25is extended through an opening in the lamination Ila and through theupper slot 24 in the lamination Hb to receive a washer 26 which isloosely held against the lamination I'Ib bypeen ing over the rivet inthe usual manner. This arrangement permits relative sliding movement tooccur between the two laminations Ila J and l'lb while restraining thesame against deformation in either direction independent of each other.Thus, a mechanical system is provided which minimizes oscillation of theupper end of arm H in response to release of the arm followingdeformationthereof. At its extended upper end, the spring arm laminationHa is provided with bent over ears: disposed at. an angle ofapproximately s'eventy-five degrees relative to the other portions ofthe arm which are spaced apart to define an opening or slot 29 forreceiving the contact ferrule of the other pigtail conductor formingapart of the fuse link assembly I5. This opening extends throughout thelength of the ears 2? and 28 and into the upper end portion of the armin the manner best illustrated in Fig. 8 of the drawings.

As indicated above, the mounting piece 20 is arranged to coact with an.eye bolt 2| in mounting the arm ll upon the trans-former bushing studit. As best shown in Fig. 2 of the draw ings, the eye of this bolt isarranged to enter an eye receiving slot provided at the upper end of thestud l8 and is threaded to receive a nut .2111

which is used in pulling the eye into the slot to clamp the shank 20b ofthe mounting piece '20 against one side of the stud It. Preferably theshank 20b of the mounting :piece 211 is of round cross sectionalconfiguration in order to permit the arm H to be singularly adjustedabout its iongitudi'nal axis so that it is readily deformableflatw-ise toward the bracket '26. Protection against birds falling uponthe arm I! or the bushing stud l8 and producing a short circuit to thetransformer tank It is obtained by enclosing this stud and the major'p'or'tion of themounting piece Iii-within an inverted cup-shapedinsulator -30. Th'e'top wall 30a of this insulator is slotted to receivethe head toe of the mounting piece 20 so that it may be telescopedupward along the arm 1-! while the arm assembly is being mounted uponthe stud i8 and then dropped down after the mounting o 'aera'tion iscompleted to enclose the stud 1'3 and the ico extending part of themounting piece 20. s

Referring now more particularly tolligs. :5 and 6 of the drawings, thefuse link i5 is there illustrated as "comprising a tubular :metal casing:3l having an open lower end and a flanged upper end which isclosed bythe terminal cap 32. This cap rigidly mounts a *small metallic ferrule33 within which is solder-connected one end of a pigtail conductor 34.This flexible LEllQtEJl-l conductor extends away, from the end'cap 32and is provided "at its extended end with a ferrule-35 The ferrule 35isand a manipulating loop 36. provided with a conical part 3 5a adaptedfor wedging engagement with the ears 2"! and 280i the springarm l1 inthe manner more fully explained below. :Preferably, the ferrule v:33 employed in electrically and mechanically connect ing the pigtailconductor 34 to the end cap 32 is inserted through an opening in thiscap and is provided at its lower end with a flange 33a seated againstthe under side of the cap and solder-connected thereto,

A second pigtail conductor 31 projecting from the lower end of the linkl functions as the opposite terminal thereof. This conduptor is providedat its extended end with a contact ferfule 38 and a manipulating loop 39of different configuration from the loop 36 in order to permit the twoends of the link to be readily distinguished for the purpose statedbelow. Preferably, the configuration of the loop 39 is as shown in Fig.5 of the drawings. The ferrule 33 is provided with a conical ortion 33aadapted for wedging engagement with the ears Ito and |6b of the bracketI6 within the slot |6c between these ears.

The pigtail 34 is formed from a short length of'b'raided conductivestrands, and in the construction thereof is threaded through the ferrule35 until the length remaining at the upper end thereof is justsufficient to form a loop 36 of the desired diameter. The upper end ofthe conductor is now inserted back into the upper portion of theferrule, following which the loop and ferrule are submerged in a solderbath to impregnate. the loop portion of the cable with solder. When.this solder is .permitted to cool, the loop is stiffened, the end partof the conductor is fixedly anchored within the ferrule 35 and theferrule is rigidly anchored to the intermediate portion of the conductoradjacent the loop part thereof. Thepigtail 31 is formed in an identicalmanner, except that it differently shaped forming mandrel is employed inthe loop forming operation. The construction and mode of operation ofthe fuse link components provided Within the metallic casing 3| aresubstantially the same as disclosed and claimed in applicants priorPatent No.. 2,453,396, granted November 9, 1948, with the importantexceptions pointed out below. This casing 3| houses three fusibleelements 40, 4| and 42 which. are connected in series circuitrelationship between the, casing 3| and the pigtai],

conductor 31 The two elements 4| and 42 are both formed of Nichrome wireor another metal wire or ribbon of the desired resistivity, and are bothof the same cross sectional area, such that they. possess substantiallyidentical time-cur-v rent fusing characteristics. The fusible element 41is substantially straight throughout the maj or portion of its lengthand the lower end portion thereof is centrally disposed within the upperend portion of the stranded pigtail conductor 31, the overlappingportions of the two elements 4| and 31 being telescoped within a metalassembly sleeve 44. This sleeve is crimped adjacent the lower endthereof, as indicated at 44a, and the lower-end of the fusible element4| is brought out through the strands of the conductor 3'! and wrappedaround the conductor 37 as indicated at 4|b. After the three elements4|, 31, and 44 have been assembled to occupy the relative positionsillustratedin Fig. 6 of the drawings, the crimp 44a may be formed aroundthe lower portion of the sleeve 44 for the purpose of providing a rigidmechanical connection between the three named parts; Thereafter, thelower end portion of the sleeve 44, the adjacent portion of the pigtailconductor 31 and the wrapped end portion 4 b of the fusible element 4|may be soldered to provide a rigid connection therebetween.

"The fusible element 42 may be more properly designated a combinationimpedance element and heating element in that it functions inconjunction with the improved surge gap facilities described below toprevent surge currents of large magnitude from traversing the fusibleelements 40 and 4| and also acts to heat the fusible element 40 to afusing temperature when the link is subjected to an overload current fora sustained time interval. In order to perform these two functions theelement 42 is constructed in the form of a helically coiled conductor,and the upper end portion 42a thereof is electrically and mechanicallyconnected to the underside of the contact head 32 by crimping the samebetween the flange 3|a and the cap 32.

The convolutions of the element 42 are spaced apart axially of the tube3 and the spaced apart relationship between the turns is maintained byembedding the same in a body of dielectric refractory material 45. Thisbody is preferably formed of a refractory cement and serves severalfunctions which are pointed out with particularity below. It may, forexample, be formed of Portland cement or any ceramic material which ischemically inert, has high specific heat, and is possessed of goodelectrical insulating proper ties. In order to increase the inductanceof the element 42, thereby to enhance the surge current blockingfunction thereof, particles of magnetic material, such, for example, asiron owder or magnetite, may be dispersed throughout the body 45, but inno case should the density of the magnetic particles be such as toprovide conductive paths capable of short-circuiting the convolutions ofthe element 42. Among other functions, the body 45 serves rigidly toposition or support the turns of the element 42 Within the tube 3|, andto this end entirely fills the upper portion of the tube. It also servesto support a tubular conductor 46 centrally of the tube 3|, this elementbeing utilized in the connection of the fusible element 4| with thelower end portion of the combination heating and inductance element 42.More specifically, the upper tubular portion of the connecting element46 is projected well within the turns of the element 42 in spaced apartrelationship therefrom, and is embedded in the body 45. ment is providedwith an outwardly extending flange 46a which serves to seat the lowerturn of the element 42 in a manner such that the tubu lar portion of theelement 46 is substantially concentrically disposed within the turns ofthe element 42. This lower turn of the element 42 is electrically and.mechanically connected to the flanged portion 46a of the element 46 bymeans of a high melting point solder 41, or the like. The

upper end of the connecting element 46 is elec-- trically andmechanically connected to the upper serpentine end Ma of the fusibleelement 4| through the fusible element 40, the latter element being inthe form of a body of alloy solder having a melting point ofapproximately 365 F. It is to be noted that the fusible element 40, asthus formed Within the tubular portion of the connecting element 46, isdisposed well within the turns of the element 42 so that heat generatedby current conduction through the latter element,

may be transferred to the fusible element 40 through that portion of therefractory body 45 which separates the fusible element 40 from theadjacent turns of the element 42, Spring tension imposed upon the freelower end of the pigtail conductor 3! may be utilized to rapidlywithdraw the end 4la of the fusible element from the At its lower endthis connecting eleconnecting element 45 when the named fusible elementis heated to a melting temperature, and to widen a break in the fusibleelement 41 coca sioned by heating this element to a fusing, temperature.

For the purpose of increasing the heat storage capacity of the structureincluding the fusible element 40, a thermal storage element 48 isprovided which is arranged in heat transfer relationship with theelement 40 and the heating element 42. This element is in the .form of acopper or brass rod disposed centrally of the tubular cas ing 31 andhaving its lower end contacting the exposed upper surface of the fusibleelement 4%. It is held in an upright position in axial alignment withthe tubular conductor 46 by virtue of its being embedded in the body 45.

During prolonged use of the link, the upper portion of the fusibleelement 40 may many times be heated to a fluid state without actualrupture of the element due to lack of persistence of the currentoverload responsible for the excessive heat energy, Also repeatedheating and cooling of the body 45 may result in the formation of smallinterstices therein through which the fluid metal could be dispersed toshort-circuit the lower convolutions of the coiled conductor 4:2. Thiswould result in undesired modification of the time-overloadcharacteristic of the link. In order to obviate this possibility, aceramic insulating tube 49 is provided to act as a barrier between theparts .411, -45., and :48 and the turns of the coiled conductor elementit. Specifically, this tube is telescoped over the tubular cnductor 46to rest upon the'fiange 43c and is embedded in the body 45 in the mannerillustrated. Being of heat resistant ceramic material, the tube to isnot subject to cracking and hence acts .as a leak-proof barrier betweenthe fusible element 40 and the convolutions of the coiled conductorelement 42. Also, since the tube 49 has approximately the same heattransfer characteristics as the body 45, its presence in the zone ofheat transfer between the elements 46 and 48 and the element 42 does notseriously complicate the problem of producing links having substantiallythe same time-overload characteristics in production quantities.Further, provision of the tube 49 in the structure facilitates assemblyof the component elements of the structure in the manner explainedbelow.

In order to maintain the turns of the element 42 out of contact with themetal casing ii, to maintain the element 41 out of contact with thetubular casing 31 and to provide a support for the surge ga facilitiesdescribed below, the en-' tire assembly within the casing 3i and .a partofthe sleeve 14 are surrounded by a tube 50 formed of Bakelite or othersuitable insulating material. At its upper end, this tube is providedwith a flange 50a pressed against the metal cas ing flange am when thecap 32 is fastened to the flange 31a. This tube 59 fits snugly withinand is adhesiv'ely bonded to the tubular mem--- ber 31, and the lowerend portion 56b thereof projects outwardly from the open lower end ofthe casing 3 i. It is counterbored from the upper end to provide a firstportion 50o of large internal diameter for receiving the parts 42, 45,11 6, .418, and 49, and a second portion 50b of smaller internaldiameter for receiving the fusible element 41. The flange 45a of thetubular conductor 45 is seated upon the step 5% between these twoportions of the tube 50.

In order to assist in producing arc extinction within the tube 5.0 whenthe link is ruptured either through fusing of the element form-sing ofthe element 41, that part of the tube portion b through which thefusible element .41 extends may be lined with a gas evolving material54. Preferably, this lining is in the form of a layer of long fibercellulose adhesively secured to the inner surface of the tube portion50b between the flange 50d and the upper end of the sleeve 44 tosurround the fusible element 4:1. 7

For the purpose of preventing moisture, dirt and the like from cominginto contact with the active components of the fuse link there isprovided in accordance with the present invention a viscous sealingmaterial, preferably comprising one of the recently developed silicones,which is inserted in the space between the tube150 and the sleeve 44. Ifdesired this viscous sealing material may also fill a substantialportion of the space between the liner 5! and the fusible element 4l-toinsure good sealing action. It has been found that the use of suchmaterial in the space between the liner 5i and the fusible ele ment 4!does not interfere with are interruption and does not impede theseparation of the parts of the fuse link unon interruption thereof.

As indicated above, in order to prevent light ning surges from rupturingthe fusible heatinz element 42, a surge gap having relatively immov ableelectrodes is connected in shunt with this element. Specifically, and inaccordance with one feature of the present invention, the heat storageelement 43 having its lower end in electrical and mechanical contactwith the upper end of the fusiblebody 40, is provided with upper endwhich is spaced apart from a member 54 associated with the .cap assembly:32 in a. manner so as to define a small air gap 52 be tween the member.54 and the adjacent end of the heat storage member 48. This gap ineombination with the storage element 48 and the fusible body at providesa surge path in shunt with the heating element 42 for lay-passing surgesaround this element.

In order to assist in weatherprooflng the above described activecomponents of the l5 and more important to assist in producing arcextinction in response to rupture of the by heavy overloads, aweatherproof tube 153 is provided which is wholly supported by the cueing 3L More specifically, the upper portion of this tube as viewed inFig. 5 of the drawings is press fitted onto the casing 31 to bringthe'upper end thereof into abutting engagement with the ends of the capThe lower end or the tube 53 extends outwardly beyond the lower end .0;the insulating tube 50 to house an appreciable portion of the Pigtailconductor 3.1. In order toaid in the are extinguishing action theportion of the tube 53 below the end of the tube '58 is lined with ashort length 01 2 tube $55 preferably formed of a gas evolvinginsulating material which is pinned into position within the expul s-iontube 53 by means of a small pin '56. should be understood that the tubes'50 and :58 could comprise a single tube in which case the casing 3::would be dispensed with. Withksuch an arrangement a much longer areextinguishing section is provided without the requirement of a separateexpulsion tube. In the illustrated embodiment the two separate tubes 50and .53

are provided so that a standard fuse link may be employed whileaffording the same operation 93 when a single tube is used.

Whenthe fuse link I 5 to :tuse the cutout embodied in the protectiveapparatus shown in Figs. 1 and 2 of the drawings,'the roundconfiguration of the loop 36 provides an indication to the lineman thatthis end of the link should be connected to the upper end of the springarm H. In this regard it Will be understood that the line connection isbrought into the terminal conductor Nb of the arrester Me so that withthe apparatus unfused, a connection is first made with the dead springarm I! during the fusing operation. This connection may conveniently bemade by using the hook of a "hot-stick to position the contact ferrule35 in the channel 29 between the ears 2! and 28 with the conical part ofthis ferrule engaging the edges of the two ears. After this connectionis made, the hot-stick hook may be shifted to the loop 39 and the linkl5 pulled toward the bracket 16 to insert the contact ferrule 38 intothe slot lie between the ears [6a and [6b of this bracket. As thisoperation is performed, the spring arm I! is de-formed toward thebracket I6 in the manner illustrated in Fig. 2 of the drawings. Afterthe contact ferrule 38 is positioned between the bracket ears "5a and[6b, the pulling force exercised on the loop 39 through the hot-stickmay be relieved permitting the ferrule 38 to move into the channel "5ato bring the conical part 38a thereof into Wedging engagement with thesides of the ears I60. and 16b. Thus the fusing operation is completedthrough the performance of a relatively few simple steps.

As best shown in Fig. 2 of the drawings, with the cutout of the unitfused, the fuse link [5 is angularly disposed with respect to thehorizontal with its open end disposed in the lowermost portion. Thispositioning of the link insures against rain entering the expulsion tube53 and assists the viscous sealing material in preventing moisture, dirtand the like from coming into contact with the active components of thelink. Thus there is no necessity for housing the link to protect thesame.

As indicated above, the conical portions of the two ferrules and 38 arewedgingly engaged with the ears provided at the extended ends of thespring arm I? and the bracket [5 respectively. This wedging engagementinsures good electrical conductivity between the contact ferrules andthe spring arm and bracket without the necessity of imposing anexcessive pull upon the fusible element 40 of the link which mightdestroy the current-time characteristics thereof.

As pointed out above, the live or high voltage side of the line feedingthe transformer I0 is connected to the terminal conductor Nb of thearrester unit 14a so that current is normally fed to the transformerprimary winding over a path which includes the bracket Hi, the contactferrule 38, the pigtail conductor 31, the fusible elements 4|, 40 and 42in series, the casing terminal cap 32, the pigtail conductor 34, thecontact ferrule 35, the spring arm 11, mounting piece 20 and thetransformer bushing stud [8. The tank of the transformer it! providesthe usual ground connection. With the circuit thus arranged, thearrester Ma provides a lightning surge path between the high voltageside of the line and ground which serves to icy-pass the link 15 and theprimary winding of the transformer when li htning surges are impressedupon this side of the line. Such surges are prevented from burning outor damaging the heating element 42 of the fuse link through the actionof the facilities including the gap 52 for by-passing this element.

In this regard, it is noted that the character of the surges which maybe permitted to act upon the fusible elements 4! and 42 by the arrester14a is such that these two elements are not susceptible of beingruptured.

'In considering the mode of operation of the fuse link IE, it may beassumed that the transformer I0 is provided with a low voltage secondaryload which under normal conditions approximates the full load capacityof the trans former l0, and that this secondary load includes motors andother devices which, during the starting periods thereof, are capable ofproducing heavy transient currents of relatively short duration in boththe primary and secondary windings of the transformer Hi.- In thisregard, it will be understood that due to the heat radiatingcapabilities of the transformer parts, the transformer I may be capableof with-'- standing an overload current of reasonable magnitude, such,for example, as 200 to 300 per cent, for a relatively long timeinterval; whereas it can withstand current of the order of 500 per centof normal for only a short time interval. It will also be understoodthat the transformer is capable of being damaged by a sustained increase in the voltage applied thereto. I '1 The fuse link operates toprotect thetransformer against damage occasioned by overload currentscaused by any one of the mentioned factors. At the same time, thefuselink permits the transformer to be operated under sus= tainedoverload current conditions for a period less than that required todamage the transformer, and will not rupture when subjected to thenormal and non-injurious high cur.- rents which are produced incident tomotor start;- ing, or the like. In this regard it will be understoodthat since the three serially related elements 4! 4i and 42 of the linkit are traversed by the current flowing through the primary winding ofthe transformer, they are all heated by current conduction andrthetemperatureof each element varies with changes in the magnitude of thiscurrent. The fusible element 40 is also heated by the heat conductedthereto from the element 42 through the walls of theconnecting element46. Heat energy is also trans.- ferred from the turns of the element 42to the fusible element 4a through that portion of the refractory body 45and the tube 4% which are disposed between the tubular portion of theconnecting element -48 and the surrounding turns of the element 42, andalso from the thermal storage element 48. Under constant load currentconditions and with a constant voltage so long as the load currentthrough the secondary winding of the transformer does not substantiallyexceed the full load capacity of this transformer, the fusible element48 is operated at a temperature well below that required to producefusion thereof. When, however, the secondary load current of thetransformer gradually rises and is sustained for a period approachingthat at which the transformer will be damaged, the temperature of thefusible element 40 is raised accordingly. Thus, as the load currentincreases, the current traversing the three elements 4!), 4| and 42 iscorrespondingly increased so that more heat is produced in the fusibleelement 48 by current conduction. Concurrently the amount of heatconducted to this fusible element from the fusible elements 4! and 42 isincreased. Also concurrently, the amount of heat transferred from theturns of the element 42 to the fusible element l-ll through therefractory body 45-, and the tube id is increased. A portion of the heatenergy accumulating in the element 40 is transferred to the storageelement 48 by conduction. After av predetermined time interval, requiredfor the accumulation of heat. within the fusible element 2 3, thiselement is. heated to its fusing temperature and melts. Provision of thestorage element 48 materially increases this time interval over thatwhich would obtain in the absence of this element in the combination.When the element 4!] is thus ruptured, the fusible element 4!, thesleeve 44, and; the upper end of the pigtail conductor 31., are: quicklyexpelled. from. the lower ends of. the tubes- 3| and 56 under theinfluence of the spring arm [1, thereby rapidly to: break the circuitfor energizing the primary winding of the transformers.

During the described separation of the element 4| from the tubularconductor 45 upon fusl ng; ofv the element 40,, an arc is drawnv withinthe portion 50b of the tube 50. This: are insta-ntly heats the coating51 to gas evolving temperature, with the result that gases are evolvedtherefrom which accelerate extinction of the arc. It has been found thatprovision. of the gas evolving coating 5| permits the link itself toeftectively extinguish heavy current arcs of the; order of severalhundred ampers even when the link is: used in high voltage circuits ofseveral thousand volts.

To consider the action of the fuse link it further, it may he pointedout. that the refractory body 45 and: the tube 419 prevent the. fusibleele- Moreover, those portions of the refractory body 45 and the tube E9which are disposed between the tubular portion of the connecting element46' and the storage element 48- and the turns of the heating" element42' dissipatea largev portion of" the heat resulting from the currentsurge through the element 42 away from the element 4|. They also delaythe transmission of the increased increment of heat produced by theelement 4? to the storage element it and the ad j'acent walls of theconnecting element 46' for an interval which will normally exceed theduration of the current transient. Accordingly, the increased incrementof heat energy arriving at the surfaces of the connecting element 46 andstorage element 48 from the element 42 as a result of the momentary highcurrent, effectsan insufiicient increasein the temperature of thefusible element 49' to cause this element to melt. In other words, thetotal heat accumulated in the fusible element 40 as a resultof thetransient high current is insufficient to heat this element to itsfusing temperature; Thus it will be understood that the refractory body45 and the tube 49, or more exactly the thermal impedance of thiscomposite structure, protects: the fusible element 40 against outagesoccasioned by transient currents of the character which frequently occurin the load pattern of any transformer secondary load. This isaccomplished, moreover, without" increasing the thermal capacity of the12 fusible element 4|]v to a point such that it will provide noprotection for sustained overload currents.

The thermal impedance of the refractory bod-y the tube 59 also preventsthe fusible element- 40 from immediately rupturing when the transformeris subjected to a highcurrent, such, for example, as that; which isvproduced when the secondary winding of the transformer isshortcircuitesl- In the absence of an additional protective clement,therefore, the transformer could easily be darn-aged by an overloadcurrent of: this character during. the period required: to transfersnihcient heat from the heating element t2 to the fusible element W tocause the latter element to melt-- The second fusible element 41.functions to guard the transformer against damage when suhiected to anoverload current of this type. immediately the element ll is' subjectedto transientcurrent' of particular character just referred tor, aportion thereof lying: between the: upper end of the sleeve and thelower end the fusible element ift is heated to a fusing temperature,permi ing this element to rupture.

When the fuse it it is. ruptured in response to an overload condition ofany one of the types mentioned above, i. e., through melting of thefusible body kill or melting of the fusible element the hol'ding forcesimposediupon. the deforming' spring arm it! are instantly releasedpermittin-g this arm to swing to: the: left from it closed circuitposition illustrated in Fig. 2 0i the drawings. Incident to thisoperation the link 15 is pulled away from the pigtail 33' toproduce arcelongation within the tube 58. As the arm l- 'l swings away from the.bracket It, the tubes 31 and Ell are pulled away from the pigtail 3'5and de scribe an are above the extended end of the: arm Eff. Theelements of the link being pulled away from the element H5 obviouslygather momentum as the movement of the arm it proceeds with the resultthat when this arm stops at a position to the left of its unrestrainedposition as shown in 2 of the drawings the con-tact 35' is pulled out ofthe channel and drops to the ground. In this regard, it will be notedthat all of the components within the tube 3! which may become heated toa high temperature incident to rupture of the fuse extinction of the areare contained with-in the tube ill, the outside of which remains at alow temperature. "Hence tlii'ere is no possibility of the production ofgrass fires when the parts of the link 15 fall to the ground. When thepigtail 31 becomes disengaged' from the remaining components of the linktln'ougl i the action of the spring arm 81 in the manner just explained,it falls down over the bracket l6 and. remains in this position untilsuch time as the cutout is refused. In this regard it ispointed out thatthe length of the pig,- tail 3 7 is substantially less than the distancebetween the upper end ofthe insulator l4 and the grounded bracketssupporting this insulator so that there is no possibility of thisconductor short-oircuiting the high voltage side of the line to ground.Ihe manner in which the cutout may be refused will be clearly apparentfrom the foregoing explanation.

From the explanation it will be understood that the disclosed protectiveapparatus is exceedingly simple in arrangement, may be easily andcheaply manufactured, and yet provides positive protection againstdamage to an associated. transformer or the like when the transformer issubject to all types of overloads and lightning surges of the characternormally encountered in operating practice. Thus the cutout portion ofthe apparatus requires only three elements in addition to those normallyprovided in transformer protective equipment, namely, the small bracket16, the simple spring arm assembly l1, and the fuse link I5. All ofthese elements are of very simple construction and may be easilymanufactured at low cost. Further, the operations required in refusingthe assembly may easily be performed by relatively unskilled linemenwithout danger and in a very short time.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be understood thatvarious modifications may be made therein which are within the truespirit and scope of the invention as defined in the appended claims.

What is claimed as new and is desired to be secured by Letters Patent ofthe United States is:

1. Protective apparatus for a transformer provided with a terminalconductor extending upward from the transformer tank, comprising anelongated lightning arrestor supported at one side of said tank in asubstantially vertical position and provided with a terminal conductorat its upper end, a conductive bracket mounted upon one of said terminalconductors, and a spring arm mounted upon and extending upwardly fromthe other of said terminal conductors, said bracket and arm beingprovided with means at the extended ends thereof for mechanicallyholding the opposed terminal conductors of a fuse link and said armbeing deformable toward said bracket to permit connection of theterminal conductor of the link to said holding means and to bias thelink for are elongation in response to rupture of the fusible element ofthe link, said bracket and arm being so supported and arranged that theinner portions of the holding means thereof form a pair of acute angleswith respect to the tensioned fuse link.

2. Protective apparatus for a transformer provided with a terminalconductor extending upward from the transformer tank, comprising anelongated lightning arrestor supported to one side of said tank in asubstantially vertical posi-- tion and provided with a terminalconductor at its upper end, a conductive bracket mounted upon one ofsaid terminal conductors, and a spring arm mounted upon and extendingupwardly from the other of said terminal conductors, said bracket andarm having slots at their extended ends for receiving the terminalconductors of a fuse link and said arm being deformable toward saidbracket to permit connection of the terminal conductors of the link tosaid arm and bracket and to bias the link for are elongation in responseto rupture of the fusible element of the link, said bracket and armbeing so supported and arranged that the closed end of the slottedportions thereof form a pair of acute angles with respect to thetensioned fuse link.

3. Protective apparatus for a transformer provided with a terminalconductor extending upward from the transformer tank, comprising anelongated lightning arrestor supported to one side of said tank in asubstantially vertical position and provided with a terminal conductorat its upper end, a conductive bracket mounted upon one of said terminalconductors, a spring arm mounted upon and extending upwardly from theother of said terminal conductors, and a fuse link provided withoppositely extending pigtail conductors each provided with a ferrulehaving a conical part embracing the conductor, said bracket and said armhaving slots at their extended ends for wedgingly receiving the conicalparts of said ferrules and said arm being deformable toward said bracketto permit insertion of the conical parts of said ferrules in said slotsand to bias the link for are elongation in response to rupture of thefusible element of the link, said ferrules being so supported by theslots that said slotted ends form a pair of acute angles with thetensioned pigtail conductors whereby the wedging of the ferrules withrespect to the slots is increased.

l. Protective apparatus for a transformer provided with a terminalconductor extending upward from the transformer tank, comprising anelongated lightning arrestor supported to one side of said tank in asubstantially vertical position and provided with a terminal conductorat its upper end, a conductive bracket mounted upon one of said terminalconductors and extending away from said one terminal conductor, apartially laminated spring arm mounted upon and extending upwardly fromthe other of said terminal conductors, the laminated portion of said armextending from a point intermediate the ends of said arm to said otherterminal conductor, and a fuse link provided with oppositely extendingpigtail conductors each provided with a ferrule having a conical partembracing the conductor, said bracket and said arm having slots at theirextended ends for wedgingly receiving the conical parts of said ferrulesand said arm being deformable toward said bracket to permit insertion ofthe conical parts of said ferrules in said slots and to bias the linkfor arc elongation in response to rupture of the fusible element of thelink.

EDWARD H. YONKERS.

References Cited in the file of this patent UNI'IED STATES PATENTSNumber Name Date 2,325,555 Steinmayer July 27, 1943 2,327,865 Brown etal. Aug. 24, 1943

